Vapor deposition of single crystals



July 8, 1958 s. s. BRENNER 2,842,468

VAPOR DEPOSITION OF SINGLE CRYSTALS Filed July 20, 1955 Pi .A g

In ventor': Siegfried Sidn ey Brenner;

by 4 W /'-//'s Attorney.

VAPOR DEPOSITION or SINGLE CRYSTALS Siegfried Sidney Brenner, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 20, 1955, Serial No. 523,359

12 Claims. (Cl. 1481.6)

The present invention relates to high strength crystals and more particularly to a process whereby such crystals may be grown at or about atmospheric pressure, and is a continuation-in-part of my co-pending application Serial No. 471,075, entitled fSingle Crystals, filed November '24, 1954, now abandoned.

, Previously known crystalline materials have never exhibited values for mechanical properties, such as tensile strength, elastic limit, etc., as high as they theoretically "should. Usually, the actual strength of crystalline materials is of the order of several degrees of magnitude "less than their theoretical maximum strength. It has been postulated that thisdifferenceis primarily caused by the presence of structural imperfections in the crystal lattice, such as dislocations. It has been found that rod-like single crystals may be grown to have near-theoretical values of their mechanical properties. .Because of their high "strength,these crystals are useful as strain-gauge elements, springs, and the like.

'Ihave discovered that near-perfect single crystals may be grown at or near atmospheric pressure during the hydrogen reduction of a volatile metal compound, such as .halide, and also under the same'pressure conditions by .the thermal decomposition of a volatile compound, such as a metal halide. pressure or substantially atmospheric pressureis in- 2,842,468 Patented July 8, 1958 compound may be conveniently'placed in an open top porcelain'boat or the like and inserted'in the tube furnace. This apparatus is schematically illustrated in Fig. 1 of the drawing in which the tube furnace is conventionally 5 composed of a hard glass or ceramic tube and an elec- The phrase at or near atmospheric tendedto cover a pressure range extending from a major ,fracti'on of one atmosphere to about 'oneand one-half atmospheres.

It is therefore a principal object of myinventionto provide a process whereby rod-like high strength single crystals may be grown by deposition from the vapor phase at or near atmospheric pressure. 7

A further object of my invention is the provision of a (process whereby rod-like high strength single metal crystals maybe grown byvapor phase deposition of themetal resulting from the decomposition of a volatile metal compound. v v

Other and dilferentobjects of my invention will be- "comeapparent from the following disclosure which will be inore readily understood when read with reference to the accompanying drawing, in which Fig. 1 is a semischematic elevational view, partly in vertical section, of an embodiment of apparatus usefhlinthepractice of my invention, and Fig. 2-- is a sectional'view taken along plane zl of Fig. 1 showing details thereof in greater detail;

nace as shown.

supplied to the heating element'll.

tricaI resistance heating element 11. As is well known, such furnaces are usually provided with a thermal insulating jacket protecting the heating element, but for clarity of illustration this has been omitted in the drawing.

Tube 10 is provided with end closures 12 and 13 of any suitable material which "may be provided with tubular thermocouple 16 may be inserted, as shown. In the practice of my invention with the apparatus shown, a quantity of the volatile metal compound to be treated is placed in a suitable container such as a porcelain boat 17 and the container positioned in the hot zone of the tube fur- The temperature-sensing means 16 is placed in contact with the container and the end closures inserted in the ends of the tube 10. The furnace is heated by energizing the heating element 11 and the temperature of the container 17 is measured by means ofa thermocouple and regulated by controlling the power If the crystal growth is to be accompanied by the vapor phase reduction of a volatile metal compound, a reducing atmosphere at sub- 1 stantially atmospheric pressure is provided. I have found that hydrogen passed through the tube furnace by means of tubular members '14 and 15fprovides such an atmosphere and it may be conveniently disposed of by burning 'at the output end. As thetemperature ofthe boat is increased, the volatile metal compound contained therein "begins to vaporize and elemental rnetal'is depositedin the form of rod-like high strength single crystals upon surfaces of the boat 17 which 'are'expose d to them'etal vapor. This is illustrated in greater detail in Fig. '2, in which'a cross-section of boat 17 is shown resting within the tube It) with thermocouple 16 in contact with boat 17. The volatile metal compound is shown as a particulate mass at 18, however, it will be appreciated that at the higher temperatures employable with some ofthe" coinpo'undsto be disclosed, a liquid phase may esteemed, depending upon the particular materialbeingtreated.

The highstrength rod-like single crystals of metal 20 are deposited as shown upon the surfaces of the boat, usually but not exclusively on the inner side surfaces of the boat. in the event that a volatile metal compound is to be thermally decomposed, a reducing atmosphere is not necessary and the crystal growth as-illustrated in Fig. 2 'may be accomplished in air, providedf the material does not oxidize or otherwise react'withtheatmosphere'at the temperature employed for-"decomposition. If sucha "reaction would take place, a neutral 'pmtecavefambslnpracticing myinvention, a volatile metal compound is subjected to heatadjacenta suitable substrate, such as, for example, glass, porcelain or the like. The metal compound is vaporized, substantially simultaneously decomposed and the metal deposited from the vapor phase a phere may be provided. In any event, volatile products of either thermal decomposition or reduction are permitted to leave the reaction-zone. The reaction ing the hydrogen reduction of a volatile metal compound,

such as, for example, a metal halide, may be characterized by the equation A MeX 56H, BK Me and the thermal decomposition of a volatilecompo'u'nd, such as, for example, a metal halide, by theequatibn MeX'-- -MG+%X2 More specifically, the following table lists example of metals from which rod-like high strength single crys: tals have been grown according to my invention.

Optimum Metal Tempera- Reaction ture,0

Copper 620 CuI+ H2 Ou+HI Silver 800 AgOl+% H; Ag+HCl lron 730 FeOl +H2 Fe+2HOl Iron 760 FeBr +H Fe+2HBr Nickel 740 NiBr +H2 Ni+2HBr Cobalt 650 CoBr +gz Oo+2HBr 11 Platinum 800 P1201; Pt+2C1z 1].! Gold 550 AuOlz Au+Ol2 From the foregoing, it may be seen that the first six reactions involve the reduction of a volatile metal halide, while the last two examples illustrate thermal decomposition of volatile metal halides.

It will be noted here that the single crystals of gold listed in the foregoing table were formed during the ther- I mal decomposition of a commercially obtained sample of gold chloride for which no analysis is available, but which probably consisted of a mixture of auric chloride (AuCl and aurous chloride (AuCl). In view of the fact that the reaction temperature employed is well above the decomposition temperatures of both gold chlorides, the exact composition of the salt is believed immaterial and therefore the reaction equation has not been balanced. In this respect it should be here noted that extremely pure metal salts are not necessary in the practice of my invention. I have found that reagent grade salts are entirely satisfactory.

The temperatures given for the several reactions is about that at which optimum single crystal growth occurs. Actually, high strength copper single crystals, for example, may be grown over the range of about 430 C. to 800 C. Similarly, the temperatures listed for the I latter five examples represent values which permit about optimum growth, but which may be varied by about i 100 to 200 C. before, on the lower side, crystal growth is slowed to an impractical rate or, on the higher side, before imperfections are introduced by too rapid growth. The rate at which the reducing atmosphere is passed over the growth sites of the crystals may be varied over a substantial range. For example, hydrogen flow rates of the order of from about centimeters per minute to about 100 centimeters per minute have been successfully employed in the practice of my invention.

The crystals prepared according to my invention were removed from the furnace and tested by bending. The crystals supported elastic strains up to 1.5 a load condition requiring an elastic limit far in excess of that realizable by conventional imperfect metals. For example, annealed single crystals, conventionally prepared from such materials and similarly tested, seldom support elastic strains as high as 0.01%. 7

From the foregoing, it will be apparent that I have provided a method for producing near-perfect high strength rod-like single crystals of metals comprising the ferromagnetic group, i. e. iron, cobalt and nickel, group I(B) of the periodic table, i. e., copper, silver and gold, and platinum bythe decomposition of volatile metal compounds of these metals to permit their deposition from the vapor phase.

.In view of the known characteristics of the halogen compounds and particularly metal halides, it is contemplated that my invention may be applied to other halides of these metals as well as to halides of other metals, provided the compounds are volatile. Further, my invention may be applied to other volatile metal compounds which may be either reduced or thermally decomposed in the manner disclosed.

From the foregoing, it is apparent that I have provided a novel, useful process for producing near-perfect high Gil strength crystals. In the foregoing description of my invention, the several embodiments thereof have been cited as exemplary and I intend in the appended claims to cover all changes and modifications which do not constitute departures from the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A method for producing high strength rod-like metallic single crystals comprising the steps of providing a metal vapor by the decomposition of a volatile metal compound at substantially atmospheric pressure and depositing the metal upon a suitable substrate at a rate less than that at which imperfections are introduced thereby forming a rod-like single crystal of said metal which is capable of supporting elastic strains as high as 1.5 percent.

2. The method recited in claim 1 in which the volatile metal compound is a halide of a metal selected from the group consisting of the ferromagnetic group, group I(B) of the periodic table and platinum.

3. The method recited in claim 2 in which the decomposition is accomplished by reducing the metal halide vapor.

4. The method recited in claim 3 in which the metal halide is copper iodide and the rate of deposition is controlled by maintaining the substrate at a temperature between about 430 C. and 800 C.

5. The method recited in claim 3 in which the metal halide is silver chloride and rate of deposition is controlled by maintaining the substrate at a temperature between about 650 C. and 900 C.

6. The method recited in claim 3 in which the metal halide is iron chloride and the rate of deposition is controlled by maintaining the substrate at a temperature between about 600 C. and 900 C.

7. The method recited in claim 3 in which the metal halide is iron bromide and the rate of deposition is controlled by maintaining the substrate at a temperature between about 560 C. and 960 C.

8. The method recited in claim 3 in which the metal halide is nickel bromide and the rate of deposition is controlled by maintaining the substrate at a temperature between about 540 C. and 940 C.

9. The method recited in claim 3 in which the metal halide is cobalt bromide and the rate of deposition is controlled by maintaining the substrate at a temperature between about 450 C. and 850 C.

10. The method recited in claim 2 in which the decomposition of the metal halide is accomplished by heating.

11. The method recited in claim 2 in which the metal halide is platinum tetrachloride and the rate of deposition is controlled by maintaining the substrate at a temperature between about 650 C. to 900 C.

12. The method recited in claim 2 in which the metal halide is gold chloride and the rate of decomposition is controlled by maintaining the substate at a temperature between about 350 C. to 750 C.

References Cited in the file of this patent UNITED STATES PATENTS 1,373,038 Weber Mar. 29, 1921 1,450,464 Thompson Apr. 3, 1923 1,601,931 Van Arkel Oct. 5, 1926 1,617,161 Koref Feb. 8, 1927 2,428,600 Williams Oct. 7, 1947 2,813,811 Sears Nov. 19, 1957 FOREIGN PATENTS 26,712 Great Britain Nov. 20, 1913 577,504 Great Britain May 21, 1946 

1. A METHOD FOR PRODUCING HIGH STRENGTH ROD-LIKE METALLIC SINGLE CRYSTALS COMPRISING THE STEPS OF PROVIDING A METAL VAPOR BY THE DECOMPOSITION OF A VOLATILE METAL COMPOUND AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND DEPOSITING THE METAL UPON A SUITABLE SUBSTRATE AT A RATE LESS THAN THAT AT WHICH IMPERFECTIONS ARE INTRODUCED THEREBY FORMING A ROD-LIKE SINGLE CRYSTAL OF SAID METAL WHICH IS CAPABLE OF SUPPORTING ELASTIC STRAINS AS HIGH AS 1.5 PERCENT. 